Flight Control Lock
Stilton;
The G-2 thru 550 flight control systems are all very similar, operating on the same G-2(G-1159) type certificate developed in the mid 60's.
They have what Gulfstream calls 'manual reversion', which allows to operate the flight controls with 'old school', cables, pulleys and bell cranks, with no hydraulic pressure in the flight control system.
On engines start up you release the flight control lock prior to start, and as the first engine spools up when pressures reaches a certain number the hydraulic boosted flight controls come in to effect.
At the conclusion of the flight, on engines shut down, when the hyd press drops to a certain point you can feel the hyd flt controls cut off, and you are back in the 'manual reversion'. All the flight controls can be moved from the cockpit, or on the outside by the wind. The rudder, and occasionally the elevator, are the most easily damaged if the gust lock is not engaged during high gusty wind conditions.
Thank you for your question .. I hope I provided an understandable reply.
MotCap